1. Field of the Invention
This invention relates to a worm-type rotary means, and particularly improvements in or relating to a worm body which is engaged with a cylindrical pinion. The worm-type rotary means of this invention is applicable for compressors, vacuum pumps, fluid expansion devices and other various rotary fluid means.
2. Description of the Prior Art
With reference to FIGS. 1 and 4, the defects and problems of the conventional art will now be described hereinafter.
The techniques of the conventional art are disclosed, for example, in the French Patent Application No. 139,172, Japanese Examined Patent Publication No. 48-12203, etc.
FIG. 1 shows a mutual engagement of a cylindrical worm of a conventional compressor with a cylindrical pinion. FIG. 2 shows a view of its mutual engagement.
In FIGS. 1 and 2, teeth 2a, 2b, 2c and 2d of a cylindrical pinion 2 are engaged with grooves 1a, 1b, 1c and 1d of a worm of a cylindrical shape in an outer profile. When the worm 1 is rotated in an arrow direction 3, the pinion 2 is rotated in an arrow direction 4 or clockwisely. The grooves 1a, 1b, 1c, 1d are covered by a casing (not illustrated) which is mounted on each top of the worm helical threads. The worm groove 1a is not closed by the pinion tooth 2a, while the groove 1b is just closed by the pinion tooth 2b. Then, a certain volume of fluid is sealed in the groove 1b which is covered by two opposite flanks of the worm screw threads as well as by the casing. It is a whole fluid discharge volume. As the worm 1 is rotated, a certain air or gas volume introduced in the groove 1b is gradually compressed and discharged finally out of a discharge port (not illustrated) of the casing. The compressing process of the fluid is changed to the grooves 1c and 1d. In FIG. 1, a fluid suction area is denoted at X.
FIG. 3 is a cubic view of a whole fluid discharge volume within a groove of the worm 1. The whole fluid discharge volume is illustrated with a cubic volume having a starting surface (points A, B, C, D) and a peak E communicated to a discharge port.
Symbols I, II, III, IV show respective partitioned areas in the fluid compressing process. Symbols A, G, H, I, E show respective points contacting the pinion tooth side with the worm groove side wherein the pinion tooth is detached from the worm groove at the point E communicated to the discharge port.
In this example, three teeth of the pinion 2 are always engaged with three grooves of the worm 1. The total length of the engagement of three pinion teeth with the three worm grooves is about 1.5 times as long as that of the engagement of a pinion tooth with a worm groove as shown in I of FIG. 3, that is distance AC+Distance FD.
As seen in FIG. 3, a cubic volume of the fluid suctioned at symbol I is reduced gradually toward the point E. The whole fluid discharge volume in the conventional worm is much less than that in the worm-type rotary fluid means according to this invention. In the conventional worm, the contact of the pinion tooth side with the worm groove is not overall but partial. For example, a point K in the pinion tooth side is ended at point K'.
FIG. 4 is another example of a conventional compressor in which a disc-type worm 11 is engaged with a cylindrical pinion 12. This example has also the same defects and problems as the example of FIG. 1. In both examples the engagement of the pinion tooth with the worm groove shortens their contact length and depth. Further, since the depth of the worm groove is short and the height of the worm screw thread is low, the pinion tooth is partially engaged with the worm groove. Accordingly, the above engagement is not uniform and the effect of fluid compression is insufficient.